The invention concerns a chassis for a motorcycle including a frame with means for holding a rear wheel, a single pronged swing arm pivotally joined to the frame at the lower forward end thereof for pivotal movement about a pivot axis parallel to the axis of the rear wheel and which swing arm near its forward free end is connected with a hub carrier for supporting a forward wheel, a steering mechanism with a handle bar carrier pivotally supported on the frame and a steering linkage with at least two hinge axes perpendicular to one another and to the pivot axis of the handle bar carrier, and a spring and damping mechanism between the swing arm and the frame for damping the movement of the swing arm.
In a chassis of the aforementioned type, known from U.S. Pat. No. 4,526,249, the hub carrier is rigidly connected with an arm of the steering linkage. This arm is provided near the hub carrier with an extension directed toward the frame and connected by a ball joint to the forward end of the swing arm. Connected by another ball joint to the upper end of this steering linkage arm, lying above the forward wheel, is a second swing arm hingedly connected to the frame, so that the two swing arms, the frame and the steering linkage arm form a hinged four-cornered structure. The steering axis runs through the two ball joints and its position is so selected that its trace point, that is the intersection point of the steering axis with the ground, lies in front of the engagement point of the wheel with the ground and therefore produces a wheel position stabilizing caster.
The invention has as its object the provision of a chassis of the aforegoing type which is compact and simple in its construction and which assures an improved stabilization of the forward wheel.
This object is achieved in accordance with the invention in that the hub carrier is supported on a stub axle carried by the swing arm, in that the hub carrier is pivotable about a pivot axis perpendicular to the stub axle which pivot axis lies in a plane normal to the axis of the forward wheel and located in the forward of the middle wheel, and in that said pivot axis passes through the axis of the forward wheel.
In the chassis of the invention, the steering point of the chassis lies exactly in the middle of the forward wheel, whereas in the above described known arrangement the steering axis is displaced from the wheel middle point toward the frame. With the same inclination angle of the steering axis (as in the mechanism of the invention) this displacement reduces the possible caster and therefore lessens the stabilization effect arising from the caster. At the same time, the chassis of the invention is extremely simple in its construction. For the same caster as in the known mechanism the arrangement of the invention permits a compact construction of the motorcycle, since the forward wheel in comparison to the known arrangement can be moved rearwardly closer to the frame.
Preferably, the stub axle is rotatably supported in the swing arm for rotation about its longitudinal axis and is non-rotatably connected with a lever which in turn is connected through a double link with the frame so that the swing arm, the lever, the double link and the frame form a hinged parallelogram. It is thereby assured that in the case of spring resisted movement of the swing arm the steering axis retains its direction in space. According to a material feature of the present invention, the length of the double link can be adjustable so that the angle the steering axis forms with the vertical or horizontal plane is adjustable.
According to the construction of a very simple embodiment of the invention, the portion of the stub axle received in the hub carrier is flattened and received in a slot shaped recess running parallel to the axis of the barrel shaped hub carrier, which recess is of a "V"-shape which widens in the direction toward the fixed end of the stub axle, and in that the hub carrier and the stub axle are connected with one another by a bolt directed perpendicularly to the flat sides of the stub axle and to the walls of the slot which are parallel to the flat sides of the stub axle with the bolt passing diametrically through the hub carrier. The bolt is consequently pivotal along with the stub axle about the longitudinal axis of its stub axle. The hub carrier is pivotal about the bolt axis to the extent permitted by the slot-shaped recess. The barrel-shaped hub carrier, on the other hand, has bearing surfaces on its circumference for supporting the forward wheel.
To permit an up and down movement of the swing arm, the steering linkage must be adjustable in its length. This can be achieved in a known way in that the steering linkage includes either a knee joint or a telescoping arrangement, as explained in more detail hereinafter.
Preferably, the swing arm has a section thereof extending rearwardly from its pivot axis and engaging a part (cylinder, piston rod) of a spring leg whose other part (piston rod, cylinder) is supported by the frame. In this way, jolts applied by the street to the forward wheel are not conducted through the steering linkage to the handle bar carrier and then to the handle bars, but are instead directly conducted through the lower part of the frame to the frame.
Further features and advantages of the invention will be apparent from the following description which explains the invention by means of exemplary embodiments in conjunction with the accompanying figures.